Problems with fogging have plagued the photographic industry from its inception. Fog is a deposit of silver or dye that is not directly related to the image-forming exposure, e.g., when a developer acts upon an emulsion layer, some reduced silver is formed in areas that have not been exposed to light. Fog can be defined as a developed density that is not associated with the action of the image-forming exposure, and is usually expressed as "Dmin", the density obtained in the unexposed portions of the emulsion. A density, as normally measured, includes both that produced by fog and that produced by exposure to light. It is known in the art that the appearance of photographic fog related to intentional or unintentional reduction of silver ion (reduction sensitization) can occur during many stages of preparation of the photographic element including silver halide emulsion preparation, (spectral) chemical sensitization of the silver halide emulsion, melting and holding of the liquid silver halide emulsion melts, subsequent coating of silver halide emulsions, and prolonged natural and artificial aging of coated silver halide emulsions.
The use of sulfinic acids and seleninic acids and their alkali cation salts in silver halide emulsions as antifoggants and storage stabilizers was first described by Brunken in U.S. Pat. No. 2,057,764. It appears as though the effect seen was due to the action of sulfinates or seleninates on sulfur-containing impurities in gelatin to diminish the amount of fresh fog and fog after incubation attributed to formation of silver sulfide. Later patents which discuss sulfinates and seleninates relate to their beneficial combination effect with a limited class of disulfides, such as those of Mueller in U.S. Pat. Nos. 2,385,762; 2,438,716; 2,440,110. Mueller teaches adding both the disulfide and sulfinate after chemical sensitization to affect fresh antifogging and storage stability.
U.S. Pat. No. 3,397,986 discloses bis(p-acylamidophenyl) disulfides as useful antifoggants added before or after any optically sensitizing dyes. U.S. Pat. No. 5,219,721 discloses the addition of dichalcogenides, including bis(p-acylamidophenyl) disulfides, to a silver halide emulsion before or during chemical sensitization.
There is a continuing need for improved methods of preventing fog in photographic elements without severely impacting sensitivity.